Environmental As
Tailings Facili
sessment
Volume E-3.6
ty
Natural Risks
Ambatovy Project
42
January 2006
Geotechnical Hazards
Unforeseen geotechnical conditions could occur as an isolated event or in concert
with a seismic or hydrological event triggering:
•
A landslide in the watersheds of the tailings or water basins which could
cause overtopping or breaching of the embankments.
•
A landslide along the embankments due to poor foundation conditions,
excessive seepage (piping) and/or oversteepening of the embankments
that could cause overtopping or breaching of the embankments.
The key question for natural hazards is:
Key Question TG-1
Are the Risks of Natural Hazards to the Public
and Environment Increased as a Result of the
Tailings Facility?
3.6.5
Impact Assessment
3.6.5.1 Assessment Methods
A risk assessment was completed for natural hazards (Knight Piesold, 2005b)
using a relative ranking system. For each of the three identified natural hazards
described in Section 3.6.4, all potential hazard scenarios were first identified
according to failure mode, associated consequences and planned risk mitigations.
The residual risks for all hazard scenarios were then estimated using a relative
risk ranking system. Acceptable risks were determined according to international
standards to minimize risk to downstream public and environmental resources.
3.6.5.2 Assessment Criteria
The assessment criteria used for the assessment of natural risks are presented in
Table 3.6-1. Five categories of risk are defined by likelihood of occurrence and
magnitude of consequences. Overall risk is a product of the relative ranking for
likelihood and consequence.
